This invention relates to a silent chain and, in particular, to the structure of a guide link washer for a silent chain.
Conventionally, a silent chain is used as a power transmission chain. FIGS. 6 and 7 show an example of a typical silent chain.
As shown in the figures, silent chain 100 has a multiple link plate 102 having a pair of teeth 121. The links are interleaved in the transverse and longitudinal directions. The link plate 102 is pivotably connected by connection pin 103, composed of a pair of long and short joint pins 131 and rocker pins 132, which are inserted into pinhole 122 of link plate 102. Guide link 104 is placed on the outside of outermost link plate 102. Both ends of joint pin 131 are fixed to pinholes formed in guide link 104.
When the chain runs on a sprocket during its operation, the link plates bend and, at such time, joint pin 131 makes rolling contact with the sliding surface of 132.
Recently, silent chain power transmission has been used under high load conditions and, for this, a silent chain of high wear resistance is required. However, when a conventional silent chain is used under high load, very high contact surface pressure is generated in the contact surfaces of the joint pin and rocker pin due to their convexxe2x80x94convex contact and, as a result, pitting wear occurs in those pins. Therefore, the requirement for high wear resistance cannot be adequately satisfied by the conventional silent chain.
The increased radius of curvature of the rolling surface of each pin can decrease contact surface pressure between joint pin and rocker pin, but a larger radius of curvature reduces the bendability of the link plates and that of the entire chain. As a result, it becomes difficult for the chain to be wrapped or wound around a small diameter sprocket. Therefore, increase of radius of curvature of the rolling surface is limited to ensure bendability of the entire chain.
In a conventional silent chain, both ends of the joint pin are fixed to a guide link of higher rigidity than link plates in general, so that, when excessive tensile load, such as a prestressing load, is applied to a chain, the shear load from the link plate acts on the center part of the joint pin while stretching of the pitch of the holes in the guide row is suppressed and, as a result, the bending load acts on the joint pin and the center of the joint pin and rocker pin can warp.
This invention addresses such a conventional problem and it offers a silent chain that retains the bendability of the entire chain, reduces the surface pressure acting on the connection pin and prevents or minimizes bending of the connection pin.
In one embodiment, the connection pin of the chain of the present invention is shown in FIG. 3. In the figure, link plates 2a, 2b are mutually bent. Incidentally, the bending angle here is given as xcex1. Connection pin 3 that pivotably supports the said link plates 2a, 2b is inserted in aperture 22 formed in each of link plates 2a, 2b. 
Connection pin 3 is composed of center pin 31 placed in the center of pinhole 22 and the opposing pair of rocker pins 32 on both sides of said center pin. Both side faces of center pin 31 are curved convex, and convex curved face 32a, corresponding to side face 31a of the center pin, is formed in rocker pin 32.
For a conventional rocker joint-type silent chain (FIGS. 6 and 7), rolling contact with angle xcex1 is necessary at the contact between rocker pin 132 and joint pin 131 to produce bending angle xcex1.
Whereas in the present invention, rocker pins 32 are placed on both sides of center pin 31, as shown in FIG. 3. Therefore, if rolling contact with angle xcex1/2 for each rocker pin 32 is realized, then bending angle xcex1 can be realized between adjacent link plates 2a, 2b. 
Therefore, in the present invention, rolling contact of the rocker pin with one half of the necessary rolling contact angle suffices, so that the radius of curvature of each pin can be increased by that much; thereby, the surface pressure of the contact surface of the pin can be reduced while bendability of the entire chain is kept and wear resistance is improved.
Guide washers corresponding to each connection pin are provided to the chain of the invention and the end of the center pin is fixed to the pinhole of the guide washer. Therefore, stretching of the hole pitch of the guide row is not restricted, even if excessive tensile load, such as a prestressing load is added to a chain and the shear load from the link plate acts on the joint pin and no bending load acts on the joint pin, so that bending of the joint pin and rocker pin is prevented.
The preferred cross-section of the center pin is shaped like a Japanese drum or general ellipse. That is, a shape with the center of both side faces curved convex outward.
Convex opposing faces of the rocker pin are curved concave or convex. The entire length of the rocker pin is equal to or slightly longer than the total width of the laminated link plates and shorter than the distance between opposing guide washers in the chain width direction.
That is, in this case, guide washers are placed independently to each connection pin so that even if the entire length of the rocker pin is somewhat longer than the total width of the laminated link plates, it does not interfere with the attachment of the guide washer. In this manner, the length of the rocker pin has a large tolerance for ease of dimension control.
Whereas in a conventional silent chain, the guide link has a pair of pinholes on both of its ends (see FIGS. 6 and 7) so that it is preferable to have the entire length of the rocker pin shorter than the total width of the interleaved link plates. In such case, both ends of the rocker pin need not be too deep inside the pinholes of the outermost link plate, so that the entire length of the rocker pin needs to be close to the total width of the link plates. Because of this reason, tolerance on the rocker pin length of a conventional silent chain is tight and its dimensional control is not easy.
In the present invention, the entire length of the rocker pin is longer than the total width of the link plates, so that an effective cross-sectional area of the connection pin can be uniform across the total width of the link plates.
The guide washer can also have a blade spring portion. In such case, the elastic force of the blade spring acts in the chain width direction and a frictional force is generated between adjacent link plates in the chain width direction for high bending resistance of the chain and reduced chordal vibration of the chain.